The present invention refers to a problem in the world of flooring, where billions of dollars are spend to protect floors, such as concrete slabs or concrete floors, with or without floor coatings, from migrating moisture or moisture vapor transmission.
Water is essentially needed as an ingredient in concrete preparations. However, in the lifespan of a concrete slab, a concrete wall or any other concrete structure liquid water and also water vapor can become destructive to said concrete structure.
Concrete is prepared with water for the hydration of cement. Remaining or superfluous water will be evaporating over the time. Accordingly, after sufficient time for drying a concrete slab contains no or very little water. Particularly, in air conditioned or de-humidified buildings a concrete slab can be considered dry.
However, concrete slabs are often installed or placed directly to the ground. Naturally, there is liquid water in the ground everywhere. Typically, the liquid ground water is bound to soil particles. Additionally, water vapor and moisture does occur in between soil particles or other materials. Such moisture or moisture vapor follows gradients and thus, has the capability to move from an area of high humidity to an area of lower humidity. Accordingly, as long as there is no functional and effective water/vapor barrier placed below the concrete slab, in such slabs, sooner or later, a moisture gradient will establish and as a consequence, vapor and moisture from the ground will migrate into the pores of the concrete slab and eventually accumulate in the slab. This migration of vapor and moisture—also called moisture vapor transmission—is a serious problem for the construction industry.
A known problem with concrete slabs without additional floor covering is that, although the moisture vapor may pass through the porous concrete and dry out again, the moisture transports various salts into or through the concrete. This causes efflorescence and will lead to exfoliation or flaking of paints or plaster due to the pressure of salt crystallization. It also might lead to fractural damage and/or mechanical instability of the surface due to volume expansion by salt crystallization.
Another well-known problem by moisture vapor relates to concrete slabs with additional floor covering. Typically, a flooring system installed on top of a concrete slab has a lower or no vapor permeability than the concrete itself. Thus, as the vapor cannot easily evaporate, the amount of vapor in the concrete slab will increase over time.
The relative humidity in the concrete and below flooring can be measured by Calcium Carbide-method according to ASTM F2170 or with a moisture meter. Due to the accumulation of vapor the humidity in the concrete slab rises, most, if not all, flooring materials can be damaged or at least will change its properties and characteristics. For example, wooden floors or wooden floor coverings can and eventually will expand and buckle if exposed to high or varying humidity over a longer period of time.
Another problem caused by the high humidity and moisture vapor in the concrete slab is the changing of the pH value at the surface of the concrete, where typically adhesives and other floor covering materials are installed. Where there are high or increasing amounts of moisture vapor accumulated in the concrete slab, there is also a high likelihood of a temperature-triggered condensation. Also temperature changes due to the operation of air conditioning or simply the surrounding weather conditions may lead to condensation of the moisture vapor and, thus, the formation of liquid water in the pores of the concrete slab. As described previously such liquid water will easily dissolve various salts. By such formation of hydroxides, the pH value increases in the concrete and particularly in the liquid water in the pores of the concrete. Typically, pH values are detected ranging from pH 12 to pH 14.
All known adhesives will be influenced and most likely degrade when exposed to such high pH values. Thus, the moisture present in the concrete causes substantial damages to the flooring. In its simplest way, such damage may be a changing of colors or a discoloring of the floor coverings. It may, however, also cause adhesion problems such as blistering, loosening or delaminating the floor coverings.
As problems arising from moisture vapor transmission are well known, many strategies and systems using various components have been suggested either to avoid or cure this problem.
One approach is known from DE 10 2004 040201, where moisture vapor transmission problems are avoided by placing a waterproof and water resistant barrier below the concrete or in between humidity-containing-materials and the concrete, thereby prohibiting the entrance and accumulation of any water or moisture vapor transmission into the concrete. Such modern solutions are, however, not always promoted, for cost or other reasons. Additionally, such solutions are particularly unhelpful for renovating projects, which have to deal with more traditional and non-waterproof constructions.
WO 95/10574, alternatively, suggests a waterproofing membrane comprising a carrier membrane made of PET, PVC or PE with adhesives on both sides. This membrane is constructed to be placed on the water-bearing—so called “positive”—side. It is intended to prevent water from getting in contact with the concrete. On this “positive” side the water pressure is higher than at the “negative” side and a moisture vapor gradient will build up from the positive towards the negative side. It is particularly worth noting that the adhesives suggested in WO 95/10574 cannot insure that the membrane stays attached to the concrete, especially when moisture vapor accumulates below said membrane.
A second approach to deal with moisture vapor transmission problems is to treat the upper surface of the concrete slab, thereby hindering the accumulation of water and, thus, a change in the pH value in said surface area of the concrete. If the surface area of the concrete is not affected by any pH change, then any adhesives placed on said surface also will not be affected and thus, will not likely show any loosening, blistery or delaminating of the flooring.
The state of the art suggests in U.S. Pat. No. 5,576,065 a liquid composition, which is applied to the concrete and forms an elastomeric and water repellent overcoat. Similarly, it is known to use a moisture vapor reduction system, which primes the concrete slab with an isolating material, which can be poured onto the concrete to prevent most of the vapor emission and to form a barrier protecting the flooring against pH changes or against blistering. Typically, such isolation materials are based on materials, such as epoxy-, PU- or MMA coatings. If applied to concrete, typically a minimum of 24-hour period is needed to allow proper setting and hardening before additional flooring can be added.
Alternatively, concrete can be sealed by administering and spreading so-called surface “hardeners”, which are solutions containing typically silicate minerals such as sodium silicate or sometimes potassium silicate, and forming with the free-lime still present in the concrete a silicate mineral directly in the pores of the concrete slab. A concrete slab treated with such sealer, typically is denser and tighter, and thus reduces but never fully prevents moisture vapor transmission. If applied to concrete, a minimum of 48-hour is needed to allow proper setting and hardening before additional flooring can be added.
The main disadvantage of the existing moisture vapor reduction system is that—when the surface of the concrete slab is sealed or coated—any remaining water is just captured in the concrete below the sealed surface. Thus, even if for the moment the moisture vapor transmission rate is reduced, the water locked in the concrete still causes problems; these problems arise in the middle of the concrete slab and thus any deteriorating effect is just delayed.
Therefore, it is the object of the present invention to improve the disadvantages of the prior art and to provide a successful system for the reduction of moisture vapor. Such system for the reduction of moisture vapor should guarantee an effective avoidance of any deteriorating effects of moisture vapor in a concrete slab. Thus, it should particularly avoid efflorescence and the destabilizing effects of the salt crystallization on the concrete microstructure. It furthermore should avoid any accumulation or inclusion of free water in pores of the concrete slab and, particularly, in any pores or holes below the flooring, as only the complete avoidance of such accumulation of water or humidity and, thus, the avoidance of any pH change can guarantee a long life span of the floor covering without any loosening, delaminating, dissolving, discoloring or other deteriorating effects.